Despite local ordinances requiring fencing and locked gates for swimming pools and the immediately adjacent areas, there are an alarmingly high number of deaths and brain damage occurring to young children who fall into the pools when no one is around to assist them. Young children are irresistibly attracted to a swimming pool and are known to climb over fences and to otherwise make their way to the pool and adjacent area so that there is a continuing possibility of danger to children in the neighborhood of a pool owner
One known system for detecting an intruder (e.g., child) in the area of a swimming pool utilizes a passive infrared system which detects infrared energy emitted from the human body anywhere within a certain predetermined detection range and responsive to such detection transmits a radio frequency signal to a receiver which actuates a suitable alerting means Such a system is sold under the trade designation Poolside Alert, OPA-100, manufactured and distributed by Optex U.S.A., Inc. of Torrance, Calif.
One major difficulty with passive infrared systems is that the sensed infrared energy can come from a great variety of sources other than a human intruder, such as, for example, sunshine directly impinging upon the sensor, reflected light, or a barbecue or grill in the vicinity, for example Also, to provide full protection where a pool has access from all sides it may be necessary to provide four sets of detectors and possibly four separate power supplies to achieve full protection